Installing and Running Oracle - Oracle Essentials - page 86

V$DISPATCHER
This view contains details of the dispatcher processes used by the shared server. It
can determine how busy the dispatchers are.
V$SHARED_SERVER
This view contains details of the shared server processes used by the shared server.
It can determine how busy the servers are, to help set the floor and ceiling values
appropriately.
V$CIRCUIT
You can think of the route from a client to its dispatcher and from the dispatcher
to the shared server (using the queues) as a virtual circuit. This view details these
virtual circuits for user connections.
Database Resident Connection Pooling
With Oracle Database 11 g Release 1, Oracle introduced another type of connection
sharing that is even more efficient and scalable than shared servers. As described above,
shared servers share a number of server processes, storing session state in the SGA and
using a dispatcher to connect requests with an available shared server.
Database resident connection pools are assigned to an application, or can be pooled
across multiple applications by connection class. Initially designed for nonthreaded
systems, like PHP, a database connection pool keeps a pool of servers available for con‐
nection requests, which are assigned by a connection broker (which then gets out of the
interaction). When a server is requested, the server remains assigned to the application
until the requesting script ends or the connection is explicitly closed.
You can configure multiple pools to handle multiple applications as well as specify the
number of servers in each pool and the number of connection brokers.This architecture
removes the overhead of having to create and destroy database sessions when connec‐
tions are opened and closed as well as the creation and destruction of server processes
required with dedicated servers. In addition, database resident connection pools elim‐
inate the need for a dispatcher, as with shared servers, and the need to store session
state. Due to these differences, database resident connection pooling can provide greater
scalability for the highest level of connections to your Oracle Database.
Oracle in the Cloud
This is the fifth edition of this topic, the first edition in the era of cloud computing. The
Oracle Database is available in several flavors in the cloud, which is the subject of
Chapter 15 . Much of the discussion of installation and configuration in this chapter is
no longer relevant when you are using an Oracle Database in the cloud.